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href="/categories/Vue%E5%89%8D%E7%BD%AE%E5%9F%BA%E7%A1%80/">Vue前置基础</a></span></div><div class="meta-secondline"><span class="post-meta-separator">|</span><span data-flag-title="Vue前置JS功底"><i class="far fa-eye fa-fw post-meta-icon"></i><span class="post-meta-label">阅读量:</span><span id="twikoo_visitors"><i class="fa-solid fa-spinner fa-spin"></i></span></span></div></div></div></header><main class="layout" id="content-inner"><div id="post"><article class="post-content" id="article-container"><h2 id="1-JS值类型与引用类型的区别"><a href="#1-JS值类型与引用类型的区别" class="headerlink" title="1. JS值类型与引用类型的区别"></a>1. JS值类型与引用类型的区别</h2><h4 id="1-值类型-x2F-简单数据类型-string、number、boolean、undefined、null"><a href="#1-值类型-x2F-简单数据类型-string、number、boolean、undefined、null" class="headerlink" title="1. 值类型&#x2F;简单数据类型: string、number、boolean、undefined、null"></a>1. 值类型&#x2F;简单数据类型: string、number、boolean、undefined、null</h4><p>值存在栈中 赋值拷贝也是栈数据 修改拷贝数据对原数据没有影响</p><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> num1 = <span class="number">10</span></span><br><span class="line"><span class="keyword">let</span> num2 = num1</span><br><span class="line">num2 = <span class="number">20</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(num1, num2) <span class="comment">// 10 20</span></span><br></pre></td></tr></table></figure><h4 id="2-引用类型-x2F-复杂数据类型-Array、function、Object"><a href="#2-引用类型-x2F-复杂数据类型-Array、function、Object" class="headerlink" title="2.引用类型&#x2F;复杂数据类型: Array、function、Object"></a>2.引用类型&#x2F;复杂数据类型: Array、function、Object</h4><p>栈中存储地址 堆中存储数据 赋值时拷贝的是栈地址 修改拷贝数据(堆)对原数据有影响</p><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> num3 = [<span class="number">1</span>,<span class="number">2</span>]</span><br><span class="line"><span class="keyword">let</span> num4 = num3</span><br><span class="line">num4[<span class="number">0</span>] = <span class="number">10</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(num3, num4)</span><br></pre></td></tr></table></figure><h4 id="3-变量修改-栈与堆的区别"><a href="#3-变量修改-栈与堆的区别" class="headerlink" title="3. 变量修改 栈与堆的区别"></a>3. 变量修改 栈与堆的区别</h4><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">num4 = <span class="number">10</span></span><br><span class="line"><span class="comment">// 只是修改了栈中数据 但地址对应的数据没有影响</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(num3, num4)</span><br></pre></td></tr></table></figure><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> num = <span class="number">10</span> <span class="comment">// 测试</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">fn1</span>(<span class="params"></span>) &#123;</span><br><span class="line">    num = <span class="number">20</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">fn1</span>()</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(num) <span class="comment">// 20</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 2.</span></span><br><span class="line"><span class="keyword">let</span> arr = [<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>]</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">fn2</span>(<span class="params">arr</span>) &#123;</span><br><span class="line">    arr = <span class="number">100</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">fn2</span>()</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr) <span class="comment">// [1,2,3]</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 3.</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">fn3</span>(<span class="params">arr</span>) &#123;</span><br><span class="line">    arr[<span class="number">0</span>] = <span class="number">100</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">fn3</span>(arr)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr) <span class="comment">// [100,2,3]</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 4. </span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">fn4</span>(<span class="params"></span>) &#123;</span><br><span class="line">    arr[<span class="number">0</span>] = <span class="number">100</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">fn4</span>()</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr) <span class="comment">// [100,2,3]</span></span><br></pre></td></tr></table></figure><hr><h2 id="2-字符串方法"><a href="#2-字符串方法" class="headerlink" title="2. 字符串方法"></a>2. 字符串方法</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 1. split(,) 把字符串转换为数组 和join()相反</span></span><br><span class="line"><span class="keyword">let</span> n1 = <span class="string">&#x27;red, blue&#x27;</span> </span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n1.<span class="title function_">split</span>(<span class="string">&#x27;,&#x27;</span>))</span><br><span class="line"><span class="comment">// 2. replace(&#x27;替换前的字符&#x27;, &#x27;替换后的字符&#x27;)</span></span><br><span class="line"><span class="keyword">let</span> n2 = <span class="string">&#x27;蔡徐坤&#x27;</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n2.<span class="title function_">replace</span>(<span class="string">&#x27;蔡&#x27;</span>, <span class="string">&#x27;嗯&#x27;</span>))</span><br><span class="line"><span class="comment">// 删除某个字符 把字符替换为空字符</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n2.<span class="title function_">replace</span>(<span class="string">&#x27;蔡&#x27;</span>, <span class="string">&#x27;&#x27;</span>))</span><br><span class="line"><span class="comment">// 应用场景:</span></span><br><span class="line"><span class="comment">// 1. 名字替换为 xx先生</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n2.<span class="title function_">replace</span>(<span class="string">&#x27;徐坤&#x27;</span>, <span class="string">&#x27;先生&#x27;</span>))</span><br><span class="line"><span class="comment">// 2. 敏感词替换</span></span><br><span class="line"><span class="keyword">let</span> n3 = <span class="string">&#x27;你是傻逼&#x27;</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n3.<span class="title function_">replace</span>(<span class="string">&#x27;傻逼&#x27;</span>, <span class="string">&#x27;**&#x27;</span>))</span><br></pre></td></tr></table></figure><hr><h2 id="3-数组的增删改查方法以及返回值"><a href="#3-数组的增删改查方法以及返回值" class="headerlink" title="3. 数组的增删改查方法以及返回值"></a>3. 数组的增删改查方法以及返回值</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> arr = [<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>,<span class="number">4</span>]</span><br><span class="line"><span class="number">1.</span> 新增数组</span><br><span class="line"><span class="comment">// .push 在数组最后面添加元素, 返回值是新数组的长度</span></span><br><span class="line"><span class="comment">// .unshift 在数组最前面面添加元素, 返回值是新数组的长度</span></span><br><span class="line">arr.<span class="title function_">push</span>(<span class="number">11</span>, <span class="number">22</span>)</span><br><span class="line">arr.<span class="title function_">unshift</span>(<span class="number">0</span>)</span><br><span class="line"><span class="number">2.</span> 删除数组</span><br><span class="line"><span class="comment">// .pop 删除数据的最后一个元素, 返回值是删除的那个元素</span></span><br><span class="line"><span class="comment">// .shift 删除数据的最前一个元素, 返回值是删除的那个元素</span></span><br><span class="line">arr.<span class="title function_">pop</span>()</span><br><span class="line">arr.<span class="title function_">shift</span>() </span><br><span class="line"><span class="number">3.</span> 查询数组</span><br><span class="line"><span class="comment">// .slice(起始下标, 结束下标), 返回 起始下标&lt;=范围下标&lt;结束下标 的数组</span></span><br><span class="line"><span class="comment">// .splice(起始下标, 删除数量, ...删除位置新增的元素)</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr.<span class="title function_">slice</span>(<span class="number">1</span>, <span class="number">3</span>))</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr.<span class="title function_">splice</span>(<span class="number">1</span>, <span class="number">1</span>))</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr)</span><br><span class="line"><span class="number">4.</span> 数组.<span class="title function_">join</span>(<span class="string">&#x27;分隔符&#x27;</span>) 将数组每一个元素用分隔符拼接成字符串</span><br><span class="line"><span class="comment">// 应用场景: 将商品标签 [&#x27;自营&#x27;, &#x27;进口&#x27;] 转换为 自营|进口</span></span><br><span class="line"><span class="comment">// 应用场景: 将演出歌手 [&#x27;周杰伦&#x27;, &#x27;周慧妹&#x27;] 转换为 周杰伦$$周慧妹</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr.<span class="title function_">join</span>(<span class="string">&#x27;|&#x27;</span>))</span><br><span class="line"><span class="number">5.</span> 数组.<span class="property">reverse</span> 翻转数组(修改原数组)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr.<span class="title function_">reverse</span>(arr))</span><br><span class="line"><span class="comment">// 应用场景: 翻转字符串</span></span><br><span class="line"><span class="keyword">let</span> a = <span class="string">&#x27;蔡徐坤&#x27;</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(a.<span class="title function_">split</span>(<span class="string">&#x27;&#x27;</span>).<span class="title function_">reverse</span>(<span class="string">&#x27;&#x27;</span>).<span class="title function_">join</span>(<span class="string">&#x27;&#x27;</span>))</span><br><span class="line"><span class="number">6.</span> .<span class="property">sort</span> 数组排序 按照<span class="variable constant_">ASCII</span>编码顺序排序</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(arr.<span class="title function_">sort</span>())</span><br><span class="line"><span class="comment">// 两个引用数据类型, 是不比较堆数据的, 只比较栈地址</span></span><br><span class="line"><span class="keyword">let</span> obj = [</span><br><span class="line">    &#123;<span class="attr">name</span>: <span class="string">&#x27;华为&#x27;</span>, <span class="attr">age</span>: <span class="number">10</span>&#125;,</span><br><span class="line">    &#123;<span class="attr">name</span>: <span class="string">&#x27;小米&#x27;</span>, <span class="attr">age</span>: <span class="number">40</span>&#125;,</span><br><span class="line">    &#123;<span class="attr">name</span>: <span class="string">&#x27;苹果&#x27;</span>, <span class="attr">age</span>: <span class="number">30</span>&#125;</span><br><span class="line">]</span><br><span class="line">obj.<span class="title function_">sort</span>(<span class="function">(<span class="params">a, b</span>) =&gt;</span> &#123;</span><br><span class="line">    <span class="keyword">return</span> a.<span class="property">age</span> - b.<span class="property">age</span> <span class="comment">// 从小到大排序</span></span><br><span class="line">&#125;)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(obj)</span><br></pre></td></tr></table></figure><hr><h2 id="4-数组的遍历方法"><a href="#4-数组的遍历方法" class="headerlink" title="4. 数组的遍历方法"></a>4. 数组的遍历方法</h2><h3 id="1-数组forEach-是没有return的也没有返回值"><a href="#1-数组forEach-是没有return的也没有返回值" class="headerlink" title="1. 数组forEach 是没有return的也没有返回值"></a>1. 数组forEach 是没有return的也没有返回值</h3><ol><li>应用场景: 修改数组的每一个元素值</li><li>金典面试题: 如何终止forEach? (try-catch)</li></ol><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// forEach 用来遍历数组对象</span></span><br><span class="line"><span class="comment">// 加强版for循环</span></span><br><span class="line"><span class="keyword">let</span> arr = [<span class="string">&#x27;小米&#x27;</span>,<span class="string">&#x27;苹果&#x27;</span>,<span class="string">&#x27;华为&#x27;</span>]</span><br><span class="line">arr.<span class="title function_">forEach</span>(<span class="keyword">function</span> (<span class="params">item, index</span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(item) <span class="comment">// 数组元素</span></span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(index) <span class="comment">// 数组下标</span></span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure><h3 id="2-数组map"><a href="#2-数组map" class="headerlink" title="2. 数组map"></a>2. 数组map</h3><ol><li>return 会新数组返回值</li><li>应用场景: 数组的转换: 根据数组的元素, 得到一个全新的数组</li><li>由于map创建一个新数组, 在没有使用返回的数组情况下调用它是不恰当的:</li><li>应该使用forEach或for…of作为代替</li></ol><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> arr = [<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>]</span><br><span class="line">arr.<span class="title function_">map</span>(<span class="function"><span class="params">i</span> =&gt;</span> &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(i)</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(&#123;<span class="attr">name</span>: i&#125;) <span class="comment">// 数组的转换</span></span><br><span class="line">&#125;)</span><br></pre></td></tr></table></figure><h3 id="2-数组filter"><a href="#2-数组filter" class="headerlink" title="2. 数组filter"></a>2. 数组filter</h3><ol><li>return true: 满足筛选条件的 放入新数组中</li><li>return true: 不满足筛选条件的 不放入新数组</li><li>filter方法自身返回值: 满足条件的新数组</li></ol><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 1. 筛选20以上的数组</span></span><br><span class="line"><span class="keyword">let</span> n1 = [<span class="number">10</span>, <span class="number">15</span>, <span class="number">20</span>, <span class="number">30</span>]</span><br><span class="line"><span class="keyword">let</span> fn = n1.<span class="title function_">filter</span>(<span class="keyword">function</span> (<span class="params">a, b</span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(a) <span class="comment">// 数组元素</span></span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(b) <span class="comment">// 数组下标</span></span><br><span class="line">    <span class="comment">// 筛选20以上的数组</span></span><br><span class="line">    <span class="keyword">return</span> a &gt;= <span class="number">20</span></span><br><span class="line">&#125;)</span><br><span class="line"><span class="comment">// 2. 筛选完 会创建符合条件的新数组 </span></span><br><span class="line"><span class="comment">// 不符合条件则返回空数组</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(fn) <span class="comment">// [20, 30]</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 3. 箭头函数写法</span></span><br><span class="line"><span class="keyword">let</span> say = n1.<span class="title function_">filter</span>(<span class="function"><span class="params">item</span> =&gt;</span> item &gt;= <span class="number">40</span>)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(say)</span><br></pre></td></tr></table></figure><h3 id="3-数组-indexOf-查找元素下标-只能找值类型下标"><a href="#3-数组-indexOf-查找元素下标-只能找值类型下标" class="headerlink" title="3. 数组 indexOf(): 查找元素下标(只能找值类型下标)"></a>3. 数组 indexOf(): 查找元素下标(只能找值类型下标)</h3><h3 id="4-数组-findIndex-查找元素下标-只能找引用类型下标"><a href="#4-数组-findIndex-查找元素下标-只能找引用类型下标" class="headerlink" title="4. 数组 findIndex(): 查找元素下标(只能找引用类型下标)"></a>4. 数组 findIndex(): 查找元素下标(只能找引用类型下标)</h3><ol><li>return true: 找到了, 循环结束, 返回当前元素下标</li><li>return false: 没找到, 循环继续, 最终返回-1</li><li>findIndex方法自身返回值: 元素下标 || -1</li><li>应用场景: 找到对象元素中 元素的下标</li></ol><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> arr = [</span><br><span class="line">    &#123;<span class="attr">name</span>: <span class="string">&#x27;小东&#x27;</span>, <span class="attr">age</span>: <span class="number">1</span>&#125;,</span><br><span class="line">    &#123;<span class="attr">name</span>: <span class="string">&#x27;小刚&#x27;</span>, <span class="attr">age</span>: <span class="number">2</span>&#125;,</span><br><span class="line">    &#123;<span class="attr">name</span>: <span class="string">&#x27;小明&#x27;</span>, <span class="attr">age</span>: <span class="number">3</span>&#125;</span><br><span class="line">]</span><br><span class="line"><span class="keyword">let</span> n1 = arr.<span class="title function_">findIndex</span>(<span class="function">(<span class="params">item, index</span>) =&gt;</span> &#123;</span><br><span class="line">    <span class="keyword">return</span> item.<span class="property">age</span> == <span class="number">2</span></span><br><span class="line">&#125;)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n1) <span class="comment">// 1</span></span><br></pre></td></tr></table></figure><h3 id="5-数组find和findIndex作用是一样的-返回值是元素本身"><a href="#5-数组find和findIndex作用是一样的-返回值是元素本身" class="headerlink" title="5. 数组find和findIndex作用是一样的, 返回值是元素本身"></a>5. 数组find和findIndex作用是一样的, 返回值是元素本身</h3><ol><li>应用场景: 修改对象数组中某一个对象属性</li></ol><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> n2 = arr.<span class="title function_">find</span>(<span class="function">(<span class="params">item, index</span>) =&gt;</span> &#123;</span><br><span class="line">    <span class="keyword">return</span> item.<span class="property">age</span> == <span class="number">2</span></span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(item) <span class="comment">// 所有对象</span></span><br><span class="line">&#125;)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n2) <span class="comment">// 返回小刚对象</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n2.<span class="property">age</span> *= <span class="number">0.1</span>) <span class="comment">// 0.2</span></span><br></pre></td></tr></table></figure><h3 id="6-数组reduce方法"><a href="#6-数组reduce方法" class="headerlink" title="6. 数组reduce方法"></a>6. 数组reduce方法</h3><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// reduce累计器 返回累计处理的结果 用于求和..</span></span><br><span class="line"><span class="keyword">let</span> n4 = [<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>,<span class="number">4</span>]</span><br><span class="line"><span class="comment">// reduce(function (上一次值, 当前值)&#123;&#125;, 初始值</span></span><br><span class="line"><span class="comment">// 1. 没有初始值</span></span><br><span class="line"><span class="keyword">let</span> n5 = n4.<span class="title function_">reduce</span>(<span class="keyword">function</span> (<span class="params">a, b</span>) &#123;</span><br><span class="line">    <span class="keyword">return</span> a + b</span><br><span class="line">&#125;)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n5)</span><br><span class="line"><span class="comment">// 2. 有初始值</span></span><br><span class="line"><span class="keyword">let</span> n6 = n4.<span class="title function_">reduce</span>(<span class="keyword">function</span> (<span class="params">a, b</span>) &#123;</span><br><span class="line">    <span class="keyword">return</span> a + b</span><br><span class="line">&#125;, <span class="number">10</span>) <span class="comment">// 初始值</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n6)</span><br><span class="line"><span class="comment">// 箭头函数写法</span></span><br><span class="line"><span class="keyword">let</span> n7 = n4.<span class="title function_">reduce</span>(<span class="function">(<span class="params">a, b</span>) =&gt;</span> a + b, <span class="number">10</span>)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n7)</span><br><span class="line"><span class="comment">// 3. reduce 执行过程</span></span><br><span class="line"><span class="comment">// 01. 没有初始值 </span></span><br><span class="line"><span class="comment">// 上一次值是数组的第一个值</span></span><br><span class="line"><span class="comment">// 每一次循环 就会把返回值给下一次循环的上一次值</span></span><br><span class="line"><span class="keyword">let</span> n8 = [<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>]</span><br><span class="line"><span class="keyword">let</span> n9 = n8.<span class="title function_">reduce</span>(<span class="function">(<span class="params">a, b</span>) =&gt;</span> a + b)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n9)</span><br><span class="line"><span class="comment">// 上一次值  当前值  返回值  (第一次循环)</span></span><br><span class="line"><span class="comment">//    1       2       3</span></span><br><span class="line"><span class="comment">// 上一次值  当前值  返回值  (第二次循环)</span></span><br><span class="line"><span class="comment">//    3       3       6 </span></span><br><span class="line"><span class="comment">// 02. 有初始值 把初始值做为上一次值</span></span><br><span class="line"><span class="keyword">let</span> n10 = [<span class="number">1</span>,<span class="number">2</span>]</span><br><span class="line"><span class="keyword">let</span> n11 = n10.<span class="title function_">reduce</span>(<span class="function">(<span class="params">a, b</span>) =&gt;</span> a + b, <span class="number">10</span>)</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n11)</span><br><span class="line"><span class="comment">// 上一次值  当前值  返回值  (第一次循环)</span></span><br><span class="line"><span class="comment">//    10       1      11 </span></span><br><span class="line"><span class="comment">// 上一次值  当前值  返回值  (第二次循环)</span></span><br><span class="line"><span class="comment">//    11       13     13 </span></span><br></pre></td></tr></table></figure><hr><h2 id="5-箭头函数和普通函数的区别"><a href="#5-箭头函数和普通函数的区别" class="headerlink" title="5. 箭头函数和普通函数的区别"></a>5. 箭头函数和普通函数的区别</h2><ul><li>this指向不同</li></ul><h3 id="1-function函数的this指向-谁调用函数-this就指向谁"><a href="#1-function函数的this指向-谁调用函数-this就指向谁" class="headerlink" title="1. function函数的this指向: 谁调用函数, this就指向谁"></a>1. function函数的this指向: 谁调用函数, this就指向谁</h3><ol><li>普通函数: fn() this指向window</li><li>对象方法: fn.方法名() this指向对象</li><li>构造函数: new 函数名 this指向实例对象</li></ol><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">function</span> <span class="title function_">fn</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>)</span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">fn</span>() <span class="comment">// window</span></span><br><span class="line"><span class="keyword">let</span> obj = &#123;</span><br><span class="line">    <span class="attr">a</span>: fn</span><br><span class="line">&#125;</span><br><span class="line">obj.<span class="title function_">a</span>() <span class="comment">// 指向obj</span></span><br><span class="line"><span class="keyword">new</span> <span class="title function_">fn</span>() <span class="comment">// 指向fn</span></span><br></pre></td></tr></table></figure><h3 id="2-箭头函数this-箭头函数没有this-本质是访问上级作用域this"><a href="#2-箭头函数this-箭头函数没有this-本质是访问上级作用域this" class="headerlink" title="2. 箭头函数this: 箭头函数没有this 本质是访问上级作用域this"></a>2. 箭头函数this: 箭头函数没有this 本质是访问上级作用域this</h3><ol><li>箭头函数不能作为构造函数(报错)</li><li>箭头函数不能使用上下文修改this(call、apply、bind)</li><li>箭头函数不能使用arguments(报错)</li></ol><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> <span class="title function_">f</span> = (<span class="params"></span>) =&gt; &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>)</span><br><span class="line">&#125;</span><br><span class="line">f.<span class="title function_">call</span>(<span class="string">&#x27;你好&#x27;</span>) <span class="comment">// 还是window</span></span><br></pre></td></tr></table></figure><h3 id="3-经典面试题"><a href="#3-经典面试题" class="headerlink" title="3. 经典面试题"></a>3. 经典面试题</h3><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> obj1 = &#123;</span><br><span class="line">    <span class="attr">name</span>: <span class="string">&#x27;小明&#x27;</span>,</span><br><span class="line">    <span class="title function_">age</span>(<span class="params"></span>) &#123; <span class="comment">// 等价于 age function() &#123;&#125;</span></span><br><span class="line">        <span class="keyword">function</span> <span class="title function_">fn1</span>(<span class="params"></span>) &#123;</span><br><span class="line">            <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>) <span class="comment">// 指向window</span></span><br><span class="line">        &#125;</span><br><span class="line">        <span class="title function_">fn1</span>()</span><br><span class="line">        <span class="keyword">let</span> <span class="title function_">fn2</span> = (<span class="params"></span>) =&gt; &#123;</span><br><span class="line">            <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>) <span class="comment">// 指向obj1 fn1跟fn2平级作用域</span></span><br><span class="line">        &#125;</span><br><span class="line">        <span class="title function_">fn2</span>()</span><br><span class="line">    &#125;,</span><br><span class="line">    <span class="attr">say</span>: <span class="function">() =&gt;</span> &#123; <span class="comment">// say是箭头函数 this指向上级window</span></span><br><span class="line">        <span class="keyword">function</span> <span class="title function_">fn1</span>(<span class="params"></span>) &#123;</span><br><span class="line">            <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>) <span class="comment">// 指向window</span></span><br><span class="line">        &#125;</span><br><span class="line">        <span class="title function_">fn1</span>()</span><br><span class="line">        <span class="keyword">let</span> <span class="title function_">fn2</span> = (<span class="params"></span>) =&gt; &#123;</span><br><span class="line">            <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>) <span class="comment">// 指向window</span></span><br><span class="line">        &#125;</span><br><span class="line">        <span class="title function_">fn2</span>()</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line">obj1.<span class="title function_">age</span>()</span><br><span class="line">obj1.<span class="title function_">say</span>()</span><br></pre></td></tr></table></figure><hr><h2 id="6-原型与原型链"><a href="#6-原型与原型链" class="headerlink" title="6. 原型与原型链"></a>6. 原型与原型链</h2><ol><li>对象原型__proto__的意义是为对象成员查找机制提供一条路线</li><li>原型链是一个查找规则</li><li>可查找一些属性和方法 沿着一条路走</li><li>先看当前原型对象上面有没有</li><li>果没有再往上一层的原型对象查找</li><li>如果有 就可使用</li><li>往上查找最终找到Object为止(null)</li></ol><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 1. 原型链</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">fn</span>(<span class="params"></span>) &#123;</span><br><span class="line"></span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">let</span> n1 = <span class="keyword">new</span> <span class="title function_">fn</span>()</span><br><span class="line"><span class="comment">// new的实例化对象等于fn.prototype</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n1.<span class="property">__proto__</span> == fn.<span class="property"><span class="keyword">prototype</span></span>)</span><br><span class="line"></span><br><span class="line"><span class="comment">// 因为Object也是构造函数 那么就有prototype和constructor</span></span><br><span class="line"><span class="comment">// fn.protptype里的__proto__就等于 Object.constructor</span></span><br><span class="line"><span class="comment">// Object.constructor 在指回Obj 所以__proto__指向Object</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(fn.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">__proto__</span> == <span class="title class_">Object</span>.<span class="property"><span class="keyword">prototype</span></span>)</span><br><span class="line"></span><br><span class="line"><span class="comment">// Object的对象有prototype 那么protytype就一定有__proto__</span></span><br><span class="line"><span class="comment">// Object对象最大 所以指向null</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="title class_">Object</span>.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">__proto__</span>) <span class="comment">// null</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 2. instanceof运算符用于检测构造函数prototype属性</span></span><br><span class="line"><span class="comment">// 是否出现在某个实例对象的原型对象上</span></span><br><span class="line"><span class="comment">// n1 属于 fn</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n1 <span class="keyword">instanceof</span> fn) <span class="comment">// true</span></span><br><span class="line"><span class="comment">// n1 属于 Object</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n1 <span class="keyword">instanceof</span> <span class="title class_">Object</span>) <span class="comment">// true</span></span><br><span class="line"><span class="comment">// n1 不属于 Array</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(n1 <span class="keyword">instanceof</span> <span class="title class_">Array</span>) <span class="comment">// false</span></span><br><span class="line"><span class="comment">// 数组 属于 Array</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>([<span class="number">1</span>,<span class="number">2</span>,<span class="number">3</span>] <span class="keyword">instanceof</span> <span class="title class_">Array</span>) <span class="comment">// true</span></span><br><span class="line"><span class="comment">// 数组 属于 Object</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="title class_">Array</span> <span class="keyword">instanceof</span> <span class="title class_">Object</span>) <span class="comment">// true</span></span><br></pre></td></tr></table></figure></article><div 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class="item-headline"><i class="fas fa-stream"></i><span>目录</span><span class="toc-percentage"></span></div><div class="toc-content"><ol class="toc"><li class="toc-item toc-level-2"><a class="toc-link" href="#1-JS%E5%80%BC%E7%B1%BB%E5%9E%8B%E4%B8%8E%E5%BC%95%E7%94%A8%E7%B1%BB%E5%9E%8B%E7%9A%84%E5%8C%BA%E5%88%AB"><span class="toc-number">1.</span> <span class="toc-text">1. JS值类型与引用类型的区别</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#1-%E5%80%BC%E7%B1%BB%E5%9E%8B-x2F-%E7%AE%80%E5%8D%95%E6%95%B0%E6%8D%AE%E7%B1%BB%E5%9E%8B-string%E3%80%81number%E3%80%81boolean%E3%80%81undefined%E3%80%81null"><span class="toc-number">1.0.1.</span> <span class="toc-text">1. 值类型&#x2F;简单数据类型: string、number、boolean、undefined、null</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#2-%E5%BC%95%E7%94%A8%E7%B1%BB%E5%9E%8B-x2F-%E5%A4%8D%E6%9D%82%E6%95%B0%E6%8D%AE%E7%B1%BB%E5%9E%8B-Array%E3%80%81function%E3%80%81Object"><span class="toc-number">1.0.2.</span> <span class="toc-text">2.引用类型&#x2F;复杂数据类型: Array、function、Object</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#3-%E5%8F%98%E9%87%8F%E4%BF%AE%E6%94%B9-%E6%A0%88%E4%B8%8E%E5%A0%86%E7%9A%84%E5%8C%BA%E5%88%AB"><span class="toc-number">1.0.3.</span> <span class="toc-text">3. 变量修改 栈与堆的区别</span></a></li></ol></li></ol><li class="toc-item toc-level-2"><a class="toc-link" href="#2-%E5%AD%97%E7%AC%A6%E4%B8%B2%E6%96%B9%E6%B3%95"><span class="toc-number">2.</span> <span class="toc-text">2. 字符串方法</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#3-%E6%95%B0%E7%BB%84%E7%9A%84%E5%A2%9E%E5%88%A0%E6%94%B9%E6%9F%A5%E6%96%B9%E6%B3%95%E4%BB%A5%E5%8F%8A%E8%BF%94%E5%9B%9E%E5%80%BC"><span class="toc-number">3.</span> <span class="toc-text">3. 数组的增删改查方法以及返回值</span></a></li><li class="toc-item toc-level-2"><a class="toc-link" href="#4-%E6%95%B0%E7%BB%84%E7%9A%84%E9%81%8D%E5%8E%86%E6%96%B9%E6%B3%95"><span class="toc-number">4.</span> <span class="toc-text">4. 数组的遍历方法</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#1-%E6%95%B0%E7%BB%84forEach-%E6%98%AF%E6%B2%A1%E6%9C%89return%E7%9A%84%E4%B9%9F%E6%B2%A1%E6%9C%89%E8%BF%94%E5%9B%9E%E5%80%BC"><span class="toc-number">4.1.</span> <span class="toc-text">1. 数组forEach 是没有return的也没有返回值</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#2-%E6%95%B0%E7%BB%84map"><span class="toc-number">4.2.</span> <span class="toc-text">2. 数组map</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#2-%E6%95%B0%E7%BB%84filter"><span class="toc-number">4.3.</span> <span class="toc-text">2. 数组filter</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#3-%E6%95%B0%E7%BB%84-indexOf-%E6%9F%A5%E6%89%BE%E5%85%83%E7%B4%A0%E4%B8%8B%E6%A0%87-%E5%8F%AA%E8%83%BD%E6%89%BE%E5%80%BC%E7%B1%BB%E5%9E%8B%E4%B8%8B%E6%A0%87"><span class="toc-number">4.4.</span> <span class="toc-text">3. 数组 indexOf(): 查找元素下标(只能找值类型下标)</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#4-%E6%95%B0%E7%BB%84-findIndex-%E6%9F%A5%E6%89%BE%E5%85%83%E7%B4%A0%E4%B8%8B%E6%A0%87-%E5%8F%AA%E8%83%BD%E6%89%BE%E5%BC%95%E7%94%A8%E7%B1%BB%E5%9E%8B%E4%B8%8B%E6%A0%87"><span class="toc-number">4.5.</span> <span class="toc-text">4. 数组 findIndex(): 查找元素下标(只能找引用类型下标)</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#5-%E6%95%B0%E7%BB%84find%E5%92%8CfindIndex%E4%BD%9C%E7%94%A8%E6%98%AF%E4%B8%80%E6%A0%B7%E7%9A%84-%E8%BF%94%E5%9B%9E%E5%80%BC%E6%98%AF%E5%85%83%E7%B4%A0%E6%9C%AC%E8%BA%AB"><span class="toc-number">4.6.</span> <span class="toc-text">5. 数组find和findIndex作用是一样的, 返回值是元素本身</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#6-%E6%95%B0%E7%BB%84reduce%E6%96%B9%E6%B3%95"><span class="toc-number">4.7.</span> <span class="toc-text">6. 数组reduce方法</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#5-%E7%AE%AD%E5%A4%B4%E5%87%BD%E6%95%B0%E5%92%8C%E6%99%AE%E9%80%9A%E5%87%BD%E6%95%B0%E7%9A%84%E5%8C%BA%E5%88%AB"><span class="toc-number">5.</span> <span class="toc-text">5. 箭头函数和普通函数的区别</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#1-function%E5%87%BD%E6%95%B0%E7%9A%84this%E6%8C%87%E5%90%91-%E8%B0%81%E8%B0%83%E7%94%A8%E5%87%BD%E6%95%B0-this%E5%B0%B1%E6%8C%87%E5%90%91%E8%B0%81"><span class="toc-number">5.1.</span> <span class="toc-text">1. function函数的this指向: 谁调用函数, this就指向谁</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#2-%E7%AE%AD%E5%A4%B4%E5%87%BD%E6%95%B0this-%E7%AE%AD%E5%A4%B4%E5%87%BD%E6%95%B0%E6%B2%A1%E6%9C%89this-%E6%9C%AC%E8%B4%A8%E6%98%AF%E8%AE%BF%E9%97%AE%E4%B8%8A%E7%BA%A7%E4%BD%9C%E7%94%A8%E5%9F%9Fthis"><span class="toc-number">5.2.</span> <span class="toc-text">2. 箭头函数this: 箭头函数没有this 本质是访问上级作用域this</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#3-%E7%BB%8F%E5%85%B8%E9%9D%A2%E8%AF%95%E9%A2%98"><span class="toc-number">5.3.</span> <span class="toc-text">3. 经典面试题</span></a></li></ol></li><li class="toc-item toc-level-2"><a class="toc-link" href="#6-%E5%8E%9F%E5%9E%8B%E4%B8%8E%E5%8E%9F%E5%9E%8B%E9%93%BE"><span class="toc-number">6.</span> 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